GJ 9827 c

(Imaginary Picture of GJ9827 c: Ryusuke Kuroki, Fuka Takagi & Yosuke A. Yamashiki)

GJ9827 (also known as K2-135) is a K6 type star (with a surface temperature of 4255K, a mass and radius about 0.7 times that of our Sun) about 100 light-years away from the Earth. It was discovered by the transit method during the K2 mission (the second mission of the Kepler Space Telescope). Scientists found three Super-Earths (planets with a mass and radius several times that of the Earth) orbiting the star, reported in the Astronomical Journal published in February 2018. These three Super-Earths (GJ9827b, GJ9827c, GJ9827d in order of closeness to the host star) have radii of 1.62 times, 1.27 times, and 2.07 times the Earth, and their orbits around the host star are 1.2 days, 3.6 days, and 6.2 days, respectively.

The planet is a suitable candidate for more detailed observation of its planetary atmosphere using the James Web Space Telescope (JWST), which will be launched in a few years. These observations of Super-Earth atmospheres are said to be the key to understanding the atmospheric and internal structure of these types of planets, which are located at the boundary between the terrestrial planets (rocky planets) and gaseous planets, such as Jupiter. This is why the GJ9827 planetary system is so promising.

Journal Articles

1.) A System of Three Super Earths Transiting the Late K-Dwarf GJ 9827 at 30 pc

2.) Mass determination of the 1:3:5 near-resonant planets transiting GJ 9827 (K2-135)

3.) HD 106315 and GJ 9827: Understanding the Formation and Evolution of Small Planets

WEB Articles

1.) Planet GJ 9827 c

2.) THREE POSSIBLE SUPER-EARTHS DISCOVERED AROUND NEARBY SUN-LIKE STAR

3.) Planetary System GJ 9827, Secrets Of Far-Away Super-Earth

HAT-P-20b

HAT-P20b orbits  its host star at around P = 2.875317 ± 0.000004d, transit epoch Tc = 2455080.92661 ± 0.00021 (BJDUTC), with a transit time of 0.0770 ± 0.0008d. It orbits a medium bright V = 11.339 K3 dwarf GSC 1910-00239. The host star has a mass of 0.76 ± 0.03M⊙, a radius of 0.69 ± 0.02R⊙, an effective temperature of 4595 ± 80K, and a metallicity of [Fe / H] = + 0.35 ± 0.08. The mass of the planet is 7.246 ± 0.187 MJ, with a radius of 0.867 ± 0.033 RJ, and an average density of 13.78 ± 1.50 g cm-3, which is the second-highest of all known exoplanets.

Journal Articles

1.) HAT-P-20b–HAT-P-23b: FOUR MASSIVE TRANSITING EXTRASOLAR PLANETS

WEB Articles

1.) Planet HAT-P-20 b

HATS-17b

HATS-17b is a warm planet with a mass close to that of  Jupiter, that orbits around a Sun-like star about once every 16.255 days. The host star of HATS-17b has ~1.13 times the mass and ~1.09 times the radius of the Sun. Additionally, the host star’s surface temperature is estimated to be 5846 ± 78 K and the luminosity is about 25 percent greater than the Sun. By measuring how much light the plant blocks when it transits its host star, the radius of HATS-17b is estimated to be 0.777 ± 0.056 times the radius of Jupiter.

When radial velocity measurements were used, HATS-17b seemed to be 1.338 ± 0.065 times the mass of Jupiter. Knowing the size and mass of the planet, the density of HATS-17b can be calculated and is found to be ~3.50 g/cm³, roughly 30 percent denser than aluminum. The density of HATS-17b is remarkably high for an object with its mass. For comparison, the mean density of Jupiter is 1.326 g/cm³.

Interior models of HATS-17b suggest that ~50 percent of the planet’s mass is composed of a massive core of heavier elements. This works out to be around 200 times the mass of Earth. The massive core of HATS-17b is consistent with the high metallicity of its parent star. A star’s metallicity refers to the abundance of elements heavier than hydrogen and helium. The host star of HATS-17b has roughly twice the metallicity of the Sun and a more metal-rich protoplanetary disk can form massive cores more efficiently.

The host star HATS-17 has an apparent magnitude of 12.4, with an absolute magnitude of 4.75. It is 1.13 times more massive and 1.09 times larger compared with our sun. The surface temperature is 5846 K with a spectral type of G. In this planetary system, the extrasolar planet HATS-17 b orbits around the star HATS-17 with its orbital distance of 0.1308.

Journal Articles

1.) HATS-17b: A TRANSITING COMPACT WARM JUPITER IN A 16.3 DAYS CIRCULAR ORBIT

WEB Articles

1.) HATS-17b is a Warm-Jupiter Denser than Aluminium

2.) Our research: HATS-17b: a transiting compact warm Jupiter in a 16.3 days circular orbit

HD 219134 b

While it may not have a catchy name, HD 219134 b is the nearest known rocky planet outside our solar system and it deserves our attention.

The planet orbits the star HD 219134, which is visible to the human eye near the constellation Cassiopeia, only 21 light-years from the sun. Like our own solar system with Mercury, Venus, Earth, and Mars, HD 219134 b has three planetary siblings.

What makes HD 219134 b special is how near it is to us – relatively speaking. We can learn a lot about these close exoplanets by using techniques that would be difficult or impossible for those at greater distances.

For example, using a technique called the radial velocity method it’s possible to deduce an exoplanet’s mass by measuring tiny movements of the star caused by the exoplanet’s gravitational pull. This reveals that HD 219134 b has a mass of between four and five times that of the Earth, making it a type of exoplanet known as a “Super-Earth.”

Journal Articles

1.) Bayesian analysis of interiors of HD 219134b, Kepler-10b, Kepler-93b, CoRoT-7b, 55 Cnc e, and HD 97658b using stellar abundance proxies

2.) The HARPS-N Rocky Planet Search I. HD 219134 b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun

3.) A SIX-PLANET SYSTEM ORBITING HD 219134

WEB Articles

1.) It’s not Earth 2.0, but our new rocky neighbour is a planet worth watching

HD219134 c

HD 219134 c is a Super-Earth exoplanet that orbits a K-type star. Its mass is about 4.36 times Earth’s, it takes 6.8 days to complete one orbit of its star, and it is 0.0653 AU from its host star. Its discovery was announced in 2015.

Journal Articles

1.) A 12-YEAR ACTIVITY CYCLE FOR THE NEARBY PLANET HOST STAR HD 219134

2.) A SIX-PLANET SYSTEM ORBITING HD 219134

3.) Secondary atmospheres on HD 219134 b and c

WEB Articles

1.) HD 219134: A Nearby System with Multiple Transits

2.) HD 219134 c